<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>CSS</title>
</head>

<body>

  <style>
    /* 去掉下划线 */
    a {
      text-decoration: none;
    }

    /* 加上下划线 */
    .one {
      text-decoration: underline;
    }

    .two {
      text-decoration: line-through;
    }
  </style>

  <a href="#">这是一个超链接</a>

  <div class="one">这是一段话</div>

  <div class="two">这是删除线</div>
</body>

</html>